fix plint warnings, re-structure transfer code

src/finam/tools/connect_helper.py

 """Iterative connection helpers."""
+import copy
 import logging
 
 from finam.interfaces import ComponentStatus, Loggable
@@ -13,22 +14,30 @@ class MissingInfoError(Exception):
 
 
 class InfoSource:
+    """Base class for info transfer rules from inputs or outputs"""
+
     def __init__(self, name, *fields):
         self.name = name
-        self.fields = fields
+        self.fields = list(*fields) or []
 
 
 class FromInput(InfoSource):
+    """Info transfer rule from an input"""
+
     def __init__(self, name, *fields):
         super().__init__(name, fields)
 
 
 class FromOutput(InfoSource):
+    """Info transfer rule from an output"""
+
     def __init__(self, name, *fields):
         super().__init__(name, fields)
 
 
 class FromValue:
+    """Info transfer rule from a given value"""
+
     def __init__(self, field, value):
         self.field = field
         self.value = value
@@ -110,16 +119,19 @@ class ConnectHelper(Loggable):
                 in_info = self.in_infos[rule.name]
                 if in_info is None:
                     raise MissingInfoError()
-                for field in rule.fields:
-                    info.__setattr__(field, in_info.__getattr__(field))
+                _transfer_fields(in_info, info, rule.fields)
             elif isinstance(rule, FromOutput):
                 out_info = self.out_infos[rule.name]
                 if out_info is None:
                     raise MissingInfoError()
-                for field in rule.fields:
-                    info.__setattr__(field, out_info.__getattr__(field))
+                _transfer_fields(out_info, info, rule.fields)
             elif isinstance(rule, FromValue):
-                info.__setattr__(field, rule.value)
+                if rule.field == "time":
+                    info.time = rule.value
+                elif rule.field == "grid":
+                    info.grid = rule.value
+                else:
+                    info.meta[rule.field] = rule.value
 
         return info
 
@@ -145,7 +157,7 @@ class ConnectHelper(Loggable):
             raise ValueError(
                 f"No input named '{rule.name}' to use in info transfer rule."
             )
-        if isinstance(rule, FromOutput) and rule.name not in self._inputs:
+        if isinstance(rule, FromOutput) and rule.name not in self._outputs:
             raise ValueError(
                 f"No output named '{rule.name}' to use in info transfer rule."
             )
@@ -240,21 +252,9 @@ class ConnectHelper(Loggable):
         push_infos = {k: v for k, v in push_infos.items() if self.out_infos[k] is None}
         push_data = {k: v for k, v in push_data.items() if not self.data_pushed[k]}
 
-        for name, rules in self._in_info_rules.items():
-            if self.in_infos[name] is None and name not in self._in_info_cache:
-                try:
-                    info = self._apply_rules(rules)
-                    exchange_infos[name] = info
-                except MissingInfoError:
-                    pass
-
-        for name, rules in self._out_info_rules.items():
-            if self.out_infos[name] is None and name not in self._out_info_cache:
-                try:
-                    info = self._apply_rules(rules)
-                    push_infos[name] = info
-                except MissingInfoError:
-                    pass
+        # Try to generate infos from transfer rules
+        exchange_infos.update(self._apply_in_info_rules())
+        push_infos.update(self._apply_out_info_rules())
 
         if self._cache:
             self._in_info_cache.update(exchange_infos)
@@ -305,6 +305,28 @@ class ConnectHelper(Loggable):
 
         return ComponentStatus.CONNECTING_IDLE
 
+    def _apply_in_info_rules(self):
+        exchange_infos = {}
+        for name, rules in self._in_info_rules.items():
+            if self.in_infos[name] is None and name not in self._in_info_cache:
+                try:
+                    info = self._apply_rules(rules)
+                    exchange_infos[name] = info
+                except MissingInfoError:
+                    pass
+        return exchange_infos
+
+    def _apply_out_info_rules(self):
+        push_infos = {}
+        for name, rules in self._out_info_rules.items():
+            if not self.infos_pushed[name] and name not in self._out_info_cache:
+                try:
+                    info = self._apply_rules(rules)
+                    push_infos[name] = info
+                except MissingInfoError:
+                    pass
+        return push_infos
+
     def _check_names(self, exchange_infos, push_infos, push_data):
         for name in exchange_infos:
             if name not in self._inputs:
@@ -371,3 +393,18 @@ class ConnectHelper(Loggable):
                         self.logger.debug("Failed to push output data for %s", name)
 
         return any_done
+
+
+def _transfer_fields(source_info, target_info, fields):
+    if len(fields) == 0:
+        target_info.time = source_info.time
+        target_info.grid = source_info.grid
+        target_info.meta = copy.copy(source_info.meta)
+    else:
+        for field in fields:
+            if field == "time":
+                target_info.time = source_info.time
+            elif field == "grid":
+                target_info.grid = source_info.grid
+            else:
+                target_info.meta[field] = source_info.meta[field]